gcc/ada/sem_attr.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                             S E M _ A T T R                              --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2015, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
  17 --                                                                          --
  18 -- You should have received a copy of the GNU General Public License along  --
  19 -- with this program; see file COPYING3.  If not see                        --
  20 -- <http://www.gnu.org/licenses/>.                                          --
  21 --                                                                          --
  22 -- GNAT was originally developed  by the GNAT team at  New York University. --
  23 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  24 --                                                                          --
  25 ------------------------------------------------------------------------------
  26
  27 --  Attribute handling is isolated in a separate package to ease the addition
  28 --  of implementation defined attributes. Logically this processing belongs
  29 --  in chapter 4. See Sem_Ch4 for a description of the relation of the
  30 --  Analyze and Resolve routines for expression components.
  31
  32 --  This spec also documents all GNAT implementation defined pragmas
  33
  34 with Exp_Tss; use Exp_Tss;
  35 with Namet;   use Namet;
  36 with Snames;  use Snames;
  37 with Types;   use Types;
  38
  39 package Sem_Attr is
  40
  41    -----------------------------------------
  42    -- Implementation Dependent Attributes --
  43    -----------------------------------------
  44
  45    --  This section describes the implementation dependent attributes provided
  46    --  in GNAT, as well as constructing an array of flags indicating which
  47    --  attributes these are.
  48
  49    Attribute_Impl_Def : Attribute_Class_Array := Attribute_Class_Array'(
  50
  51       ------------------
  52       -- Abort_Signal --
  53       ------------------
  54
  55       Attribute_Abort_Signal => True,
  56       --  Standard'Abort_Signal (Standard is the only allowed prefix) provides
  57       --  the entity for the special exception used to signal task abort or
  58       --  asynchronous transfer of control. Normally this attribute should only
  59       --  be used in the tasking runtime (it is highly peculiar, and completely
  60       --  outside the normal semantics of Ada, for a user program to intercept
  61       --  the abort exception).
  62
  63       ------------------
  64       -- Address_Size --
  65       ------------------
  66
  67       Attribute_Address_Size => True,
  68       --  Standard'Address_Size (Standard is the only allowed prefix) is
  69       --  a static constant giving the number of bits in an Address. It
  70       --  is used primarily for constructing the definition of Memory_Size
  71       --  in package Standard, but may be freely used in user programs.
  72       --  This is a static attribute.
  73
  74       ---------------
  75       -- Asm_Input --
  76       ---------------
  77
  78       Attribute_Asm_Input => True,
  79       --  Used only in conjunction with the Asm subprograms in package
  80       --  Machine_Code to construct machine instructions. See documentation
  81       --  in package Machine_Code in file s-maccod.ads.
  82
  83       ----------------
  84       -- Asm_Output --
  85       ----------------
  86
  87       Attribute_Asm_Output => True,
  88       --  Used only in conjunction with the Asm subprograms in package
  89       --  Machine_Code to construct machine instructions. See documentation
  90       --  in package Machine_Code in file s-maccod.ads.
  91
  92       ---------
  93       -- Bit --
  94       ---------
  95
  96       Attribute_Bit => True,
  97       --  Obj'Bit, where Obj is any object, yields the bit offset within the
  98       --  storage unit (byte) that contains the first bit of storage allocated
  99       --  for the object. The attribute value is of type Universal_Integer,
 100       --  and is always a non-negative number not exceeding the value of
 101       --  System.Storage_Unit.
 102       --
 103       --  For an object that is a variable or a constant allocated in a
 104       --  register, the value is zero. (The use of this attribute does not
 105       --  force the allocation of a variable to memory).
 106       --
 107       --  For an object that is a formal parameter, this attribute applies to
 108       --  either the matching actual parameter or to a copy of the matching
 109       --  actual parameter.
 110       --
 111       --  For an access object the value is zero. Note that Obj.all'Bit is
 112       --  subject to an Access_Check for the designated object. Similarly
 113       --  for a record component X.C'Bit is subject to a discriminant check
 114       --  and X(I).Bit and X(I1..I2)'Bit are subject to index checks.
 115       --
 116       --  This attribute is designed to be compatible with the DEC Ada
 117       --  definition and implementation of the Bit attribute.
 118
 119       ------------------
 120       -- Code_Address --
 121       ------------------
 122
 123       Attribute_Code_Address => True,
 124       --  The reference subp'Code_Address, where subp is a subprogram entity,
 125       --  gives the address of the first generated instruction for the sub-
 126       --  program. This is often, but not always the same as the 'Address
 127       --  value, which is the address to be used in a call. The differences
 128       --  occur in the case of a nested procedure (where Address yields the
 129       --  address of the trampoline code used to load the static link), and on
 130       --  some systems which use procedure descriptors (in which case Address
 131       --  yields the address of the descriptor).
 132
 133       -----------------------
 134       -- Default_Bit_Order --
 135       -----------------------
 136
 137       Attribute_Default_Bit_Order => True,
 138       --  Standard'Default_Bit_Order (Standard is the only permissible prefix)
 139       --  provides the value System.Default_Bit_Order as a Pos value (0 for
 140       --  High_Order_First, 1 for Low_Order_First). This is used to construct
 141       --  the definition of Default_Bit_Order in package System. This is a
 142       --  static attribute.
 143
 144       ----------------------------------
 145       -- Default_Scalar_Storage_Order --
 146       ----------------------------------
 147
 148       Attribute_Default_Scalar_Storage_Order => True,
 149       --  Standard'Default_Scalar_Storage_Order (Standard is the
 150       --  only permissible prefix) provides the current value of the
 151       --  default scalar storage order (as specified using pragma
 152       --  Default_Scalar_Storage_Order, or equal to Default_Bit_Order if
 153       --  unspecified) as a System.Bit_Order value. This is a static attribute.
 154
 155       -----------
 156       -- Deref --
 157       -----------
 158
 159       Attribute_Deref => True,
 160       --  typ'Deref (expr) is valid only if expr is of type System'Address.
 161       --  The result is an object of type typ that is obtained by treating the
 162       --  address as an access-to-typ value that points to the result. It is
 163       --  basically equivalent to (atyp!expr).all where atyp is an access type
 164       --  for the type.
 165
 166       ---------------
 167       -- Elab_Body --
 168       ---------------
 169
 170       Attribute_Elab_Body => True,
 171       --  This attribute can only be applied to a program unit name. It
 172       --  returns the entity for the corresponding elaboration procedure for
 173       --  elaborating the body of the referenced unit. This is used in the main
 174       --  generated elaboration procedure by the binder, and is not normally
 175       --  used in any other context, but there may be specialized situations in
 176       --  which it is useful to be able to call this elaboration procedure from
 177       --  Ada code, e.g. if it is necessary to do selective reelaboration to
 178       --  fix some error.
 179
 180       --------------------
 181       -- Elab_Subp_Body --
 182       --------------------
 183
 184       Attribute_Elab_Subp_Body => True,
 185       --  This attribute can only be applied to a library level subprogram
 186       --  name and is only relevant in CodePeer mode. It returns the entity
 187       --  for the corresponding elaboration procedure for elaborating the body
 188       --  of the referenced subprogram unit. This is used in the main generated
 189       --  elaboration procedure by the binder in CodePeer mode only.
 190
 191       ---------------
 192       -- Elab_Spec --
 193       ---------------
 194
 195       Attribute_Elab_Spec => True,
 196       --  This attribute can only be applied to a program unit name. It
 197       --  returns the entity for the corresponding elaboration procedure for
 198       --  elaborating the spec of the referenced unit. This is used in the main
 199       --  generated elaboration procedure by the binder, and is not normally
 200       --  used in any other context, but there may be specialized situations in
 201       --  which it is useful to be able to call this elaboration procedure from
 202       --  Ada code, e.g. if it is necessary to do selective reelaboration to
 203       --  fix some error.
 204
 205       ----------------
 206       -- Elaborated --
 207       ----------------
 208
 209       Attribute_Elaborated => True,
 210       --  Lunit'Elaborated, where Lunit is a library unit, yields a boolean
 211       --  value indicating whether or not the body of the designated library
 212       --  unit has been elaborated yet.
 213
 214       --------------
 215       -- Enum_Rep --
 216       --------------
 217
 218       Attribute_Enum_Rep => True,
 219       --  For every enumeration subtype S, S'Enum_Rep denotes a function
 220       --  with the following specification:
 221       --
 222       --    function S'Enum_Rep (Arg : S'Base) return universal_integer;
 223       --
 224       --  The function returns the representation value for the given
 225       --  enumeration value. This will be equal to the 'Pos value in the
 226       --  absence of an enumeration representation clause. This is a static
 227       --  attribute (i.e. the result is static if the argument is static).
 228
 229       --------------
 230       -- Enum_Val --
 231       --------------
 232
 233       Attribute_Enum_Val => True,
 234       --  For every enumeration subtype S, S'Enum_Val denotes a function with
 235       --  the following specification:
 236       --
 237       --    function S'Enum_Val (Arg : universal_integer) return S'Base;
 238       --
 239       --  This function performs the inverse transformation to Enum_Rep. Given
 240       --  a representation value for the type, it returns the corresponding
 241       --  enumeration value. Constraint_Error is raised if no value of the
 242       --  enumeration type corresponds to the given integer value.
 243
 244       -----------------
 245       -- Fixed_Value --
 246       -----------------
 247
 248       Attribute_Fixed_Value => True,
 249       --  For every fixed-point type S, S'Fixed_Value denotes a function
 250       --  with the following specification:
 251       --
 252       --    function S'Fixed_Value (Arg : universal_integer) return S;
 253       --
 254       --  The value returned is the fixed-point value V such that
 255       --
 256       --    V = Arg * S'Small
 257       --
 258       --  The effect is thus equivalent to first converting the argument to
 259       --  the integer type used to represent S, and then doing an unchecked
 260       --  conversion to the fixed-point type. This attribute is primarily
 261       --  intended for use in implementation of the input-output functions
 262       --  for fixed-point values.
 263
 264       -----------------------
 265       -- Has_Discriminants --
 266       -----------------------
 267
 268       Attribute_Has_Discriminants => True,
 269       --  Gtyp'Has_Discriminants, where Gtyp is a generic formal type, yields
 270       --  a Boolean value indicating whether or not the actual instantiation
 271       --  type has discriminants.
 272
 273       ---------
 274       -- Img --
 275       ---------
 276
 277       Attribute_Img => True,
 278       --  The 'Img function is defined for any prefix, P, that denotes an
 279       --  object of scalar type T. P'Img is equivalent to T'Image (P). This
 280       --  is convenient for debugging. For example:
 281       --
 282       --     Put_Line ("X = " & X'Img);
 283       --
 284       --  has the same meaning as the more verbose:
 285       --
 286       --     Put_Line ("X = " & Temperature_Type'Image (X));
 287       --
 288       --  where Temperature_Type is the subtype of the object X.
 289
 290       -------------------
 291       -- Integer_Value --
 292       -------------------
 293
 294       Attribute_Integer_Value => True,
 295       --  For every integer type S, S'Integer_Value denotes a function
 296       --  with the following specification:
 297       --
 298       --    function S'Integer_Value (Arg : universal_fixed) return S;
 299       --
 300       --  The value returned is the integer value V, such that
 301       --
 302       --    Arg = V * fixed-type'Small
 303       --
 304       --  The effect is thus equivalent to first doing an unchecked convert
 305       --  from the fixed-point type to its corresponding implementation type,
 306       --  and then converting the result to the target integer type. This
 307       --  attribute is primarily intended for use in implementation of the
 308       --  standard input-output functions for fixed-point values.
 309
 310       Attribute_Invalid_Value => True,
 311       --  For every scalar type, S'Invalid_Value designates an undefined value
 312       --  of the type. If possible this value is an invalid value, and in fact
 313       --  is identical to the value that would be set if Initialize_Scalars
 314       --  mode were in effect (including the behavior of its value on
 315       --  environment variables or binder switches). The intended use is to
 316       --  set a value where initialization is required (e.g. as a result of the
 317       --  coding standards in use), but logically no initialization is needed,
 318       --  and the value should never be accessed.
 319
 320       Attribute_Loop_Entry => True,
 321       --  For every object of a non-limited type, S'Loop_Entry [(Loop_Name)]
 322       --  denotes the constant value of prefix S at the point of entry into the
 323       --  related loop. The type of the attribute is the type of the prefix.
 324
 325       ------------------
 326       -- Machine_Size --
 327       ------------------
 328
 329       Attribute_Machine_Size => True,
 330       --  This attribute is identical to the Object_Size attribute. It is
 331       --  provided for compatibility with the DEC attribute of this name.
 332
 333       -----------------------
 334       -- Maximum_Alignment --
 335       -----------------------
 336
 337       Attribute_Maximum_Alignment => True,
 338       --  Standard'Maximum_Alignment (Standard is the only permissible prefix)
 339       --  provides the maximum useful alignment value for the target. This is a
 340       --  static value that can be used to specify the alignment for an object,
 341       --  guaranteeing that it is properly aligned in all cases. The time this
 342       --  is useful is when an external object is imported and its alignment
 343       --  requirements are unknown. This is a static attribute.
 344
 345       --------------------
 346       -- Mechanism_Code --
 347       --------------------
 348
 349       Attribute_Mechanism_Code => True,
 350       --  function'Mechanism_Code yields an integer code for the mechanism
 351       --  used for the result of function, and subprogram'Mechanism_Code (n)
 352       --  yields the mechanism used for formal parameter number n (a static
 353       --  integer value, 1 = first parameter). The code returned is:
 354       --
 355       --     1 = by copy (value)
 356       --     2 = by reference
 357       --     3 = by descriptor (default descriptor type)
 358       --     4 = by descriptor (UBS  unaligned bit string)
 359       --     5 = by descriptor (UBSB aligned bit string with arbitrary bounds)
 360       --     6 = by descriptor (UBA  unaligned bit array)
 361       --     7 = by descriptor (S    string, also scalar access type parameter)
 362       --     8 = by descriptor (SB   string with arbitrary bounds)
 363       --     9 = by descriptor (A    contiguous array)
 364       --    10 = by descriptor (NCA  non-contiguous array)
 365
 366       --------------------
 367       -- Null_Parameter --
 368       --------------------
 369
 370       Attribute_Null_Parameter => True,
 371       --  A reference T'Null_Parameter denotes an (imaginary) object of type
 372       --  or subtype T allocated at (machine) address zero. The attribute is
 373       --  allowed only as the default expression of a formal parameter, or
 374       --  as an actual expression of a subprogram call. In either case, the
 375       --  subprogram must be imported.
 376       --
 377       --  The identity of the object is represented by the address zero in
 378       --  the argument list, independent of the passing mechanism (explicit
 379       --  or default).
 380       --
 381       --  The reason that this capability is needed is that for a record or
 382       --  other composite object passed by reference, there is no other way
 383       --  of specifying that a zero address should be passed.
 384
 385       -----------------
 386       -- Object_Size --
 387       -----------------
 388
 389       Attribute_Object_Size => True,
 390       --  Type'Object_Size is the same as Type'Size for all types except
 391       --  fixed-point types and discrete types. For fixed-point types and
 392       --  discrete types, this attribute gives the size used for default
 393       --  allocation of objects and components of the size. See section in
 394       --  Einfo ("Handling of type'Size values") for further details.
 395
 396       -------------------------
 397       -- Passed_By_Reference --
 398       -------------------------
 399
 400       Attribute_Passed_By_Reference => True,
 401       --  T'Passed_By_Reference for any subtype T returns a boolean value that
 402       --  is true if the type is normally passed by reference and false if the
 403       --  type is normally passed by copy in calls. For scalar types, the
 404       --  result is always False and is static. For non-scalar types, the
 405       --  result is non-static (since it is computed by Gigi).
 406
 407       ------------------
 408       -- Range_Length --
 409       ------------------
 410
 411       Attribute_Range_Length => True,
 412       --  T'Range_Length for any discrete type T yields the number of values
 413       --  represented by the subtype (zero for a null range). The result is
 414       --  static for static subtypes. Note that Range_Length applied to the
 415       --  index subtype of a one dimensional array always gives the same result
 416       --  as Range applied to the array itself. The result is of type universal
 417       --  integer.
 418
 419       ---------
 420       -- Ref --
 421       ---------
 422
 423       Attribute_Ref => True,
 424       --  System.Address'Ref (Address is the only permissible prefix) is
 425       --  equivalent to System'To_Address, provided for compatibility with
 426       --  other compilers.
 427
 428       ------------------
 429       -- Storage_Unit --
 430       ------------------
 431
 432       Attribute_Storage_Unit => True,
 433       --  Standard'Storage_Unit (Standard is the only permissible prefix)
 434       --  provides the value System.Storage_Unit, and is intended primarily
 435       --  for constructing this definition in package System (see note above
 436       --  in Default_Bit_Order description). The is a static attribute.
 437
 438       ---------------
 439       -- Stub_Type --
 440       ---------------
 441
 442       Attribute_Stub_Type => True,
 443       --  The GNAT implementation of remote access-to-classwide types is
 444       --  organised as described in AARM E.4(20.t): a value of an RACW type
 445       --  (designating a remote object) is represented as a normal access
 446       --  value, pointing to a "stub" object which in turn contains the
 447       --  necessary information to contact the designated remote object. A
 448       --  call on any dispatching operation of such a stub object does the
 449       --  remote call, if necessary, using the information in the stub object
 450       --  to locate the target partition, etc.
 451       --
 452       --  For a prefix T that denotes a remote access-to-classwide type,
 453       --  T'Stub_Type denotes the type of the corresponding stub objects.
 454       --
 455       --  By construction, the layout of T'Stub_Type is identical to that of
 456       --  System.Partition_Interface.RACW_Stub_Type (see implementation notes
 457       --  in body of Exp_Dist).
 458
 459       -----------------
 460       -- Target_Name --
 461       -----------------
 462
 463       Attribute_Target_Name => True,
 464       --  Standard'Target_Name yields the string identifying the target for the
 465       --  compilation, taken from Sdefault.Target_Name.
 466
 467       ----------------
 468       -- To_Address --
 469       ----------------
 470
 471       Attribute_To_Address => True,
 472       --  System'To_Address (System is the only permissible prefix) is a
 473       --  function that takes any integer value, and converts it into an
 474       --  address value. The semantics is to first convert the integer value to
 475       --  type Integer_Address according to normal conversion rules, and then
 476       --  to convert this to an address using the same semantics as the
 477       --  System.Storage_Elements.To_Address function. The important difference
 478       --  is that this is a static attribute so it can be used in
 479       --  initializations in preelaborate packages.
 480
 481       ----------------
 482       -- Type_Class --
 483       ----------------
 484
 485       Attribute_Type_Class => True,
 486       --  T'Type_Class for any type or subtype T yields the value of the type
 487       --  class for the full type of T. If T is a generic formal type, then the
 488       --  value is the value for the corresponding actual subtype. The value of
 489       --  this attribute is of type System.Aux_DEC.Type_Class, which has the
 490       --  following definition:
 491       --
 492       --    type Type_Class is
 493       --      (Type_Class_Enumeration,
 494       --       Type_Class_Integer,
 495       --       Type_Class_Fixed_Point,
 496       --       Type_Class_Floating_Point,
 497       --       Type_Class_Array,
 498       --       Type_Class_Record,
 499       --       Type_Class_Access,
 500       --       Type_Class_Task,
 501       --       Type_Class_Address);
 502       --
 503       --  Protected types yield the value Type_Class_Task, which thus applies
 504       --  to all concurrent types. This attribute is designed to be compatible
 505       --  with the DEC Ada attribute of the same name.
 506       --
 507       --  Note: if pragma Extend_System is used to merge the definitions of
 508       --  Aux_DEC into System, then the type Type_Class can be referenced
 509       --  as an entity within System, as can its enumeration literals.
 510
 511       -----------------
 512       -- UET_Address --
 513       -----------------
 514
 515       Attribute_UET_Address => True,
 516       --  Unit'UET_Address, where Unit is a program unit, yields the address
 517       --  of the unit exception table for the specified unit. This is only
 518       --  used in the internal implementation of exception handling. See the
 519       --  implementation of unit Ada.Exceptions for details on its use.
 520
 521       ------------------------------
 522       -- Universal_Literal_String --
 523       ------------------------------
 524
 525       Attribute_Universal_Literal_String => True,
 526       --  The prefix of 'Universal_Literal_String must be a named number.
 527       --  The static result is the string consisting of the characters of
 528       --  the number as defined in the original source. This allows the
 529       --  user program to access the actual text of named numbers without
 530       --  intermediate conversions and without the need to enclose the
 531       --  strings in quotes (which would preclude their use as numbers).
 532
 533       -------------------------
 534       -- Unrestricted_Access --
 535       -------------------------
 536
 537       Attribute_Unrestricted_Access => True,
 538       --  The Unrestricted_Access attribute is similar to Access except that
 539       --  all accessibility and aliased view checks are omitted. This is very
 540       --  much a user-beware attribute. Basically its status is very similar
 541       --  to Address, for which it is a desirable replacement where the value
 542       --  desired is an access type. In other words, its effect is identical
 543       --  to first taking 'Address and then doing an unchecked conversion to
 544       --  a desired access type. Note that in GNAT, but not necessarily in
 545       --  other implementations, the use of static chains for inner level
 546       --  subprograms means that Unrestricted_Access applied to a subprogram
 547       --  yields a value that can be called as long as the subprogram is in
 548       --  scope (normal Ada 95 accessibility rules restrict this usage).
 549
 550       ---------------
 551       -- VADS_Size --
 552       ---------------
 553
 554       Attribute_VADS_Size => True,
 555       --  Typ'VADS_Size yields the Size value typically yielded by some Ada 83
 556       --  compilers. The differences between VADS_Size and Size is that for
 557       --  scalar types for which no Size has been specified, VADS_Size yields
 558       --  the Object_Size rather than the Value_Size. For example, while
 559       --  Natural'Size is typically 31, the value of Natural'VADS_Size is 32.
 560       --  For all other types, Size and VADS_Size yield the same value.
 561
 562       -------------------
 563       -- Valid_Scalars --
 564       -------------------
 565
 566       Attribute_Valid_Scalars => True,
 567       --  Obj'Valid_Scalars can be applied to any object. The result depends
 568       --  on the type of the object:
 569       --
 570       --    For a scalar type, the result is the same as obj'Valid
 571       --
 572       --    For an array object, the result is True if the result of applying
 573       --    Valid_Scalars to every component is True. For an empty array the
 574       --    result is True.
 575       --
 576       --    For a record object, the result is True if the result of applying
 577       --    Valid_Scalars to every component is True. For class-wide types,
 578       --    only the components of the base type are checked. For variant
 579       --    records, only the components actually present are checked. The
 580       --    discriminants, if any, are also checked. If there are no components
 581       --    or discriminants, the result is True.
 582       --
 583       --    For any other type that has discriminants, the result is True if
 584       --    the result of applying Valid_Scalars to each discriminant is True.
 585       --
 586       --    For all other types, the result is always True
 587       --
 588       --  A warning is given for a trivially True result, when the attribute
 589       --  is applied to an object that is not of scalar, array, or record
 590       --  type, or in the composite case if no scalar subcomponents exist. For
 591       --  a variant record, the warning is given only if none of the variants
 592       --  have scalar subcomponents. In addition, the warning is suppressed
 593       --  for private types, or generic formal types in an instance.
 594
 595       ----------------
 596       -- Value_Size --
 597       ----------------
 598
 599       Attribute_Value_Size => True,
 600       --  Type'Value_Size is the number of bits required to represent value of
 601       --  the given subtype. It is the same as Type'Size, but, unlike Size, may
 602       --  be set for non-first subtypes. See section in Einfo ("Handling of
 603       --  type'Size values") for further details.
 604
 605       ---------------
 606       -- Word_Size --
 607       ---------------
 608
 609       Attribute_Word_Size => True,
 610       --  Standard'Word_Size (Standard is the only permissible prefix)
 611       --  provides the value System.Word_Size, and is intended primarily
 612       --  for constructing this definition in package System (see note above
 613       --  in Default_Bit_Order description). This is a static attribute.
 614
 615       others => False);
 616
 617    -----------------
 618    -- Subprograms --
 619    -----------------
 620
 621    procedure Analyze_Attribute (N : Node_Id);
 622    --  Performs bottom up semantic analysis of an attribute. Note that the
 623    --  parser has already checked that type returning attributes appear only
 624    --  in appropriate contexts (i.e. in subtype marks, or as prefixes for
 625    --  other attributes).
 626
 627    function Name_Implies_Lvalue_Prefix (Nam : Name_Id) return Boolean;
 628    --  Determine whether the name of an attribute reference categorizes its
 629    --  prefix as an lvalue. The following attributes fall under this bracket
 630    --  by directly or indirectly modifying their prefixes.
 631    --     Access
 632    --     Address
 633    --     Input
 634    --     Read
 635    --     Unchecked_Access
 636    --     Unrestricted_Access
 637
 638    procedure Resolve_Attribute (N : Node_Id; Typ : Entity_Id);
 639    --  Performs type resolution of attribute. If the attribute yields a
 640    --  universal value, mark its type as that of the context. On the other
 641    --  hand, if the context itself is universal (as in T'Val (T'Pos (X)), mark
 642    --  the type as being the largest type of that class that can be used at
 643    --  run-time. This is correct since either the value gets folded (in which
 644    --  case it doesn't matter what type of the class we give if, since the
 645    --  folding uses universal arithmetic anyway) or it doesn't get folded (in
 646    --  which case it is going to be dealt with at runtime, and the largest type
 647    --  is right).
 648
 649    function Stream_Attribute_Available
 650      (Typ          : Entity_Id;
 651       Nam          : TSS_Name_Type;
 652       Partial_View : Entity_Id := Empty) return Boolean;
 653    --  For a limited type Typ, return True if and only if the given attribute
 654    --  is available. For Ada 2005, availability is defined by 13.13.2(36/1).
 655    --  For Ada 95, an attribute is considered to be available if it has been
 656    --  specified using an attribute definition clause for the type, or for its
 657    --  full view, or for an ancestor of either. Parameter Partial_View is used
 658    --  only internally, when checking for an attribute definition clause that
 659    --  is not visible (Ada 95 only).
 660
 661 end Sem_Attr;